The material presented as background information in this section of the specification is not necessarily prior art.
There are an increasing number of applications for lithium-ion batteries requiring high power levels. Many such battery applications require high power levels over a wide range of ambient temperatures.
For example, designers and manufacturers of automotive vehicles continually strive to improve the fuel economy of their gasoline fueled (or gasoline and alcohol fueled) or diesel fueled, multi-cylinder, reciprocating piston, internal combustion engine-driven vehicles. One approach for reducing fuel consumption in the operation of such vehicles is to stop engine operation each time that the vehicle comes to a complete stop (even a brief stop) and, then, to restart the engine when, for example, the operator releases the brake pedal or presses the gas pedal. Such continual start-stop-restart operations (start-stop, hereafter in this specification) of the vehicle engines are often managed (in different ways) by an electronic computer control module and sensors which react to the operator's stopping and starting commands.
In the many decades of usage of internal combustion engine powered vehicles, the starting of the vehicle engine was usually accomplished using a small electric starting motor powered by an electrochemical battery based on lead-lead oxide electrodes, with lead sulfate being the discharge product on each electrode, and a water-sulfuric acid electrolyte. Indeed, lead-acid batteries comprising six such cells, providing 12-14 volts DC, (called starting, lighting, and ignition batteries or SLI batteries) served to power vehicles' ignition systems, lighting systems, entertainment centers, and the like, in addition to powering engine starting. Then, during periods of suitably long engine operation, an engine-powered alternator (or generator) re-charged the vehicle's lead-acid SLI battery.
Now it is found that, with many vehicle systems for engine start-stop operation as a regular driving mode, the familiar lead-acid battery is not well suited for such frequent engine stopping and re-starting, particularly over a wide ambient temperature range. The frequent demands for relatively high motor power for engine starting and the short intervening periods for re-charging adversely affect the life and utility of lead-acid batteries.
Lithium-ion batteries offer high power density and durability for many different consumer and powered transport operations. Now, additionally, they are being considered for these continual engine start-stop vehicle applications. Lithium-ion batteries have been considered having many different combinations of electrode materials and electrolytes. However, the perceived requirements are quite demanding for a battery that is to be used on an automotive vehicle in a wide range of ambient temperature conditions for continually powering the electrical starting motor to repeatedly crank and restart an internal combustion engine.
For example, the United States Council for Automotive Research LLC, based in Southfield, Mich. (USA) (website.uscar.org) has a sub-group, U.S. Advanced Battery Consortium LLC (USABC). The USABC has issued a table of Goals for Advanced Batteries for 12V Start Stop Vehicle Applications. USABC has also issued a table of USABC Goals for Advanced Electrolytes. These goals are available online at the US CAR website. It is an object of this invention to provide a solvent for a lithium salt electrolyte that will serve effectively in a 12 volt lithium-ion battery intended for start-stop vehicle operations, and in other lithium-ion battery applications requiring high power output, especially over a broad range of operating temperatures.